I have done a lot with my MIM fretless.
It started out like this:
I then had the fingerboard epoxied by a Dutch luthier:
Then came the classy part: I switched the pickguard to a black one.
Technically, I've replaced the pickups with Fender Custom Shop 60's pickups, which I got quite cheap. They sound so incredibly awesome! Lastly, I've replaced the bridge with a Gotoh 201. The bass now looks like this:
I couldn't be happier with it. Oh wait, I can. If it had a matching headstock